1. Field of the Invention
This invention relates to an LSI circuit, and more particularly to a temperature stabilizing circuit adapted to stabilize the junction temperature of an LSI.
2. Description of the Related Art
A conventional timing generator (hereinafter referred to merely as "a T. G.", when applicable) made up of a CMOS gate array is so designed that, in the case where it is used in an LSI tester, the user can change an operating frequency every cycle at the time of measurement.
This will be described with reference to the drawing in detail. FIG. 6 is a block diagram showing a conventional T. G. made up of a CMOS gate array. FIG. 7 is a diagram indicating junction temperature and tpd in a conventional T. G. The term "tpd" as herein used is intended to mean a time difference between an input signal applied to a T. G. 61 shown in FIG. 6 and an output signal outputted by the T. G. 61. The thermal resistance of the package is 7.5.degree. C./W, the power consumption is 1 W, and the peripheral temperature is 25.degree..
In FIG. 7, at the time instant t60, the supply voltage of the LSI is an optional one. Next, when at the time instant t62 the operation is stated with 1 .mu.s, then the junction temperature becomes 32.5.degree. C. at the time instant t63. On the other hand, the tpd becomes 810 ps from 770 ps; that is, the tpd increases by 40 ps. Next, when at the time instant t64 the operation is started with 100 ns, then at the time instant t65 the junction temperature becomes 47.5.degree. C., while the tpd becomes 850 ps. Furthermore, when at the time instant t66 the operation is started with 10 ns, then at the time instant t67 the junction temperature becomes 100.degree. C., while the tpd becomes 1 ns.
In the prior art, as was described above, the T. G. 61 made up of the CMOS gate array is mounted on an LSI tester. When the user changes the operating frequency in one test, the power consumption is changed, the junction temperature is changed, and the tpd is greatly changed. And, if the tpd is greatly changed with time, the jitter value is increased, and the rated value of the LSI tester becomes worse. For instance, in FIG. 7, with the operating frequencies of 1 .mu.s and 10 ns, the jitter value is 230 ps. As is apparent from the above description, when the operating frequency of the T. G. 61 changes, the operating current is changed, and the junction temperature is changed. And the tpd of the T. G. 61 changes, and the jitter value, which is important for the LSI tester, becomes more than the rated value.